CN111025665B - a time shaper - Google Patents

Abstract

The invention provides a time shaper which is high in conversion efficiency, low in cost, simple in structure and easy to install and adjust, and aims to solve the technical problems that the existing 4F structure-based femtosecond laser pulse time shaper is low in conversion efficiency, extremely expensive in price and difficult to install and adjust, and the requirement of the femtosecond pulse time shaper on spatial postures of a beam combining mirror, a beam splitter and the like is extremely high and the installation and adjustment is difficult. Different from the traditional scheme for generating the optical path difference, the optical path difference is generated based on the difference between the refractive indexes of the optical element material and air, no moving device is arranged in the whole device, and the prism which is easy to install and adjust is adopted, so that the beam combination precision can be effectively ensured, the requirement on the space posture of the reflector is lower, and the installation and the adjustment are more convenient. Because the invention only has the transmittance attenuation among the optical elements, the loss of light energy is small, and the utilization rate of the light energy can reach more than 90 percent.

Description

a time shaper

technical field

The invention relates to the technical field of femtosecond laser pulse shaping, in particular to a time shaper.

Background technique

In various industries such as silicon processing, integrated circuit (IC) back-end processing, microelectronics packaging, and solar manufacturing, as wafer thicknesses continue to shrink, brittle materials processing faces severe challenges, and the precision (scribed lines) of their fabrication Width) and quality (edge chipping, roughness, etc.) have put forward higher requirements, which gave birth to the birth of femtosecond laser pulse shaping technology. Time shaping is to shape a laser pulse into several sub-pulses, and the time delay between sub-pulses, the number of sub-pulses, and the energy of sub-pulses can be shaped according to actual needs. Since the time-shaping femtosecond laser pulse can more flexibly and deeply affect the process of material phase transition, it provides greater convenience for the realization of high-precision, high-quality and high-efficiency material processing, especially in precision drilling, There are distinct advantages in scribing, dicing (eg glass, silicon wafer dicing) and marking.

As shown in Fig. 1, the existing femtosecond laser pulse time shaper is mainly a 4F time shaper. The incident femtosecond laser pulse is irradiated on the first grating 101 at a certain angle, and dispersion is generated in the lateral direction. The laser light is incident on the cylindrical mirror at different diffraction angles. Since the distance from the center of the grating to the center of the first lens 102 is F, the incident laser light passes through the first grating 101 and the first lens 102 to realize the time domain to frequency conversion. The Fourier transform of the domain, and the light of different frequency components are distributed sequentially in space. The phase plate 103 located on the focal plane of the first lens 102 can independently modulate light with different frequency components, and the adjustable quantities include phase, amplitude and polarization. The laser light passing through the phase plate 103 is incident on the second lens 104 and then focused on the second grating 105, compressed by the second grating 105 and then emitted, thereby realizing the conversion from the frequency domain to the time domain. Generally, the dielectric material used in this type of phase plate 103 is usually a material whose refractive index is significantly affected by light or phonons, and the control precision of the pulse delay depends on the control precision of the voltage. The 4F time shaper has advantages in the control accuracy of pulse delay, suppression of high-order dispersion, and alignment of processing light spots, but it also has obvious disadvantages: low conversion efficiency (only about 60%), sub-pulse energy / The polarization control ability is poor, the control range of the pulse delay is small, and the price is extremely expensive (the price is about 800,000). This makes it difficult to process some important transparent materials, because the processing threshold of transparent materials is very high; in addition, if the pulse delay provided is small, it also greatly limits the processing ability of femtosecond lasers for hard and brittle transparent materials.

At present, there is another femtosecond laser pulse time shaper based on the principle of optical path difference. By dividing the laser into two beams, and then adjusting the mirrors on the optical path, the two beams have different optical path differences and finally combined. This method has a high energy utilization rate, and the generated pulse delay can be adjusted, but only two sub-pulses can be generated, and the requirements for spatial attitudes such as beam combiners and beam splitters are extremely high, so it is very difficult to assemble and adjust. .

SUMMARY OF THE INVENTION

In order to solve the problem that the existing femtosecond laser pulse time shaper based on 4F structure has low conversion efficiency, extremely expensive price, and difficult installation and adjustment, and the femtosecond pulse time shaper based on the principle of optical path difference has space for beam combiner, beam splitter, etc. Due to the technical problems of extremely high posture requirements and difficult installation and adjustment, the present invention provides a time shaper with high conversion efficiency, low cost, simple structure and easy installation and adjustment.

The technical scheme of the present invention is:

A time shaper, which is special in that it includes a prism group, a reflector and a beam combiner group;

The prism group includes a first prism, a second prism, .

The beam combiner group includes a first beam combiner, ..., the N-1th beam combiner; the first beam combiner, ..., and the N-1th beam combiner are all coated with a beam splitting film;

The second prism, ..., the Nth prism is sequentially arranged on the reflected light path of the first prism, and the reflector is arranged on the transmitted light path of the first prism; or, the second prism, ..., the Nth prism is sequentially arranged on the On the transmitted light path of the first prism, the reflector is arranged on the reflected light path of the first prism;

The first beam combiner, ..., the N-1th beam combiner is sequentially arranged on the reflected light path of the reflector, and is respectively located on the reflected light path of the second prism, ..., the Nth prism.

Further, the transmitted beam of the first prism is defined as sub-pulse 1, the reflected beam of the first prism is defined as sub-pulse 2, and a diaphragm is provided on the propagation path of sub-pulse 1 and/or sub-pulse 2; N=2.

Alternatively, define the transmitted beam of the first prism as sub-pulse one, the reflected beam of the first prism as sub-pulse two, the transmitted beam of the second prism as sub-pulse three, ..., the transmitted beam of the N-1th prism as sub-pulse N ;N≥3;

A diaphragm is respectively set on the propagation path of sub-pulse 1, sub-pulse 2, sub-pulse 3..., sub-pulse N; A diaphragm is respectively provided on the propagation path of the pulse.

Further, the first prism, the second prism, ..., the Nth prism are all isosceles prisms.

Further, the size of the first prism, the second prism, . . . , the Nth prism is equal or unequal.

Further, the materials of the first prism, the second prism, . . . , and the Nth prism are the same.

Further, the diaphragm is an electronically controlled variable diaphragm.

The advantages of the present invention are:

1. High energy conversion efficiency

Since the present invention only has transmittance attenuation between optical elements, the loss of light energy is small, and the utilization rate of light energy (ie, conversion efficiency) can reach more than 90%.

2. Low cost

The invention has the advantages of simple structure, low cost, easy realization and practical application.

3. Easy to install

Different from the principle of generating optical path difference in the traditional scheme, the present invention generates optical path difference based on the difference in the refractive index of optical element material and air. There is no moving device in the whole device, and a prism that is easy to install and adjust is adopted, which can effectively ensure the beam combining accuracy. The requirements for the space posture of the reflector are lower, and the installation and adjustment are more convenient.

4. It is easy to ensure the accuracy of beam combining

For various errors existing between the existing beam splitting and beam combining, such as the angle error between the normal direction of the beam splitter and the incident light, the beam splitting ratio and the circularity of the focused spot will be caused, resulting in the energy ratio of two or more sub-pulses being different from If the deviation of 1:1 is large, or the spatial characteristics of the two sub-pulses are inconsistent (one is circular and the other is elliptical), an easy-to-adjust prism is used to make the beam easy to combine;

5. Simplified energy modulation between sub-pulses

The energy modulation between the sub-pulse sequences can be flexibly realized by adjusting the electronically controlled iris, and/or the modulation of the energy ratio of the sub-pulse sequences can be realized by designing the film layer ratio on the beam splitting surface of the prism.

6. Two or more sub-pulses can be generated, which can meet the actual needs of laser processing, broaden the laser processing capacity, and help improve the quality and efficiency of ultra-fast laser processing.

7. High precision of time shaping

Compared with the traditional scheme that uses the adjusting mirror to generate the optical path difference, the prism has a high precision of the reference plane, so the adjustment precision is higher, so the precision of the whole time shaper is higher.

Description of drawings

FIG. 1 is a schematic diagram of the existing 4F time shaper.

FIG. 2 is a schematic diagram of the principle of an embodiment of the present invention.

Description of reference numbers:

101-first grating, 102-first lens, 103-phase plate, 104-second lens, 105-second grating;

201-first isosceles prism, 202-second isosceles prism, 203-third isosceles prism, 204-first diaphragm, 205-second diaphragm, 206-reflector, 207-first beam combiner , 208-second beam combiner, 209-sub-pulse one, 210-sub-pulse two, 211-sub-pulse three.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings.

As shown in Figure 2, the time shaper of the present invention realizes time shaping based on the principle of optical path difference, and is mainly composed of an isosceles prism group, a diaphragm group, a mirror group, etc., wherein the optical path difference is mainly composed of isosceles in the optical path. The prism group is realized (the number of isosceles prisms depends on how many sub-pulses the system needs to generate), and the energy ratio between the sub-pulses is realized by an electronically controlled iris diaphragm.

Example 1:

This embodiment can generate two sub-pulses, which are composed of the optical path shown by the solid line in FIG. 2, including the first isosceles prism 201; the ultrafast laser pulse output by the femtosecond laser is incident on the first isosceles prism 201 and divided into Two paths: a first aperture 204 and a reflector 206 are sequentially arranged on the optical path (ie, the transmission light path) of the sub-pulse 209; and the second isosceles prism 202;

A first beam combiner 207 is provided at the intersection of the reflected light path of the sub-pulse 1 209 reflected by the mirror 206 and the reflected light path of the sub-pulse 210 reflected by the second isosceles prism 202;

Both the first isosceles prism 201 and the first beam combining mirror 207 are provided with semi-transmissive and semi-reflective films (the splitting ratio is 1:1).

The half-waist lengths of the first isosceles prism 201 and the second isosceles prism 202 are equal, which are all denoted as L; the difference between the refractive indices of the first isosceles prism 201 and the second isosceles prism 202 and the refractive index of air is equal , are recorded as Δn.

The ultrafast laser pulse output by the femtosecond laser enters the first isosceles prism 201, and is divided into sub-pulse 1 209 and sub-pulse 2 210 with equal energy (when the splitting ratio is 1:1). The general calculation formula of the optical path difference and time delay between the optical paths of pulse one 209 is: optical path difference △s=△n×L, time delay △t=△s/c; c is the speed of light; L is the propagation of light path length.

If n ₁ is the refractive index of air, n ₂ is the refractive index of a single isosceles prism, d is the thickness of a single mirror, n ₃ is the refractive index of a single mirror, and c is the speed of light. Then the time delay between the second sub-pulse 210 and the first sub-pulse 209 is: [(n ₂ -n ₁ )L ₁ +n ₂ L ₂ /2-n ₃ d/0.707]/c.

Sub-pulse one 209 is reflected by the mirror 206 and then incident on the first beam combining mirror 207, and sub-pulse two 210 is reflected by the second isosceles prism 202 and then incident on the first beam combining mirror 207. Since the first beam combining mirror 207 is coated with A semi-transparent and semi-reflective film is made, so the first beam combining mirror 207 can combine sub-pulse 1 209 and sub-pulse 2 210 to output, thereby obtaining sub-pulse 1 209 and sub-pulse 2 with arbitrary energy ratio and time interval Δt 210 composed of ultrafast laser pulse sequences.

If you want to adjust the energy ratio between the first sub-pulse 209 and the second sub-pulse 210, you can adjust the first aperture 204 and/or the second aperture 205; the first aperture 204 and the second aperture 205 are preferably electronically controlled Iris diaphragm.

Example 2:

As shown in the entire optical path (solid line + dotted line part) in FIG. 2 , in order to generate three sub-pulses, a semi-transparent and semi-reflective film can be coated on the reflective surface of the second isosceles prism 202, so that the second sub-pulse 210 passes through the second etc. After the waist prism 202 transmits, a sub-pulse 3 211 is obtained, and a third isosceles prism 203 is also arranged on the optical path of the sub-pulse 3 211; the reflected light path of the sub-pulse 3 211 reflected by the third isosceles prism 203 is the same as that of the sub-pulse 2 210. A second beam combining mirror 208 is also provided at the intersection of the reflected light paths reflected by the first beam combining mirror 207 .

The incident surface of the second beam combining mirror 208 is coated with a transflective film.

The half waist length of the third isosceles prism 203 is equal to that of the first isosceles prism 201 and the second isosceles prism 202, which is also L; the difference between the refractive index of the third isosceles prism 203 and the refractive index of air is also Δn.

The first sub-pulse 209 is reflected by the mirror 206 and then incident on the first beam combining mirror 207 , and the sub-pulse 2 210 is reflected by the second isosceles prism 202 and then incident on the first beam combining mirror 207 . There is a semi-permeable and semi-reflective membrane;

A part of sub-pulse one 209 is transmitted by the first beam combiner mirror 207 and then reflected by the second beam combiner mirror 208; a part of sub-pulse two 210 is reflected by the second beam combiner mirror 208 after being reflected by the first beam combiner mirror 207; Pulse three 211 is reflected by the third isosceles prism 203 and then transmitted by the second beam combining mirror 208; thus, the second beam combining mirror 208 realizes the combined beam output of sub-pulse one 209, sub-pulse two 210 and sub-pulse three 211, obtaining Sub-pulse one 209, sub-pulse two 210 and sub-pulse 211 constitute an ultrafast sub-laser pulse sequence.

If n ₁ is the refractive index of air, n ₂ is the refractive index of a single isosceles prism, d is the thickness of a single mirror, and c is the speed of light. Then the time delay between sub-pulse two 210 and sub-pulse one 209 is: [(n ₂ -n ₁ )L ₁ +n ₂ L ₂ /2-n ₃ d/0.707]/c, sub-pulse three 211 and sub-pulse two The time delay of 210 is: [(n ₂ -n ₁ )L ₁ /2-n ₃ d/0.707]/c.

In order to adjust the energy ratio conveniently, a third diaphragm (not shown in the figure) can be set on the propagation path of the third sub-pulse 211, and the third diaphragm can be located between the second isosceles prism 202 and the third isosceles prism 203. , can also be located between the third isosceles prism 203 and the second beam combiner 208 .

In practical applications, the methods of the above-mentioned Embodiments 1 and 2, and so on, can be used to realize >3 beams of sub-pulses.

Claims (7)

1. a time shaper, is characterized in that: comprise prism group, reflecting mirror and beam combining mirror group; The prism group includes a first prism, a second prism, . The beam combiner group includes a first beam combiner, ..., the N-1th beam combiner; the first beam combiner, ..., and the N-1th beam combiner are all coated with a beam splitting film; The second prism, ..., the Nth prism is sequentially arranged on the reflected light path of the first prism, and the reflector is arranged on the transmitted light path of the first prism; or, the second prism, ..., the Nth prism is sequentially arranged on the On the transmitted light path of the first prism, the reflector is arranged on the reflected light path of the first prism; The first beam combiner, ..., the N-1th beam combiner is sequentially arranged on the reflected light path of the reflector, and is respectively located on the reflected light path of the second prism, ..., the Nth prism. 2. The time shaper according to claim 1 is characterized in that: the transmitted light beam of the first prism is defined as sub-pulse one, the reflected light beam of the first prism is sub-pulse two, and in sub-pulse one and/or sub-pulse two There is a diaphragm on the propagation path; N=2. 3. The time shaper according to claim 1, wherein the transmitted beam of the first prism is defined as sub-pulse one, the reflected beam of the first prism is defined as sub-pulse two, and the transmitted beam of the second prism is defined as sub-pulse three , ..., the transmitted beam of the N-1th prism is sub-pulse N; N≥3; A diaphragm is respectively set on the propagation path of sub-pulse 1, sub-pulse 2, sub-pulse 3..., sub-pulse N; A diaphragm is respectively provided on the propagation path of the pulse. 4. The time shaper according to any one of claims 1-3, wherein the first prism, the second prism, ..., the Nth prism are all isosceles prisms. 5. The time shaper according to claim 4, characterized in that: the first prism, the second prism, ..., the Nth prism are of equal or unequal size. 6 . The time shaper according to claim 5 , wherein the first prism, the second prism, . . . , and the Nth prism have the same material. 7 . 7. The time shaper according to claim 2 or 3, wherein the diaphragm is an electronically controlled variable diaphragm.

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